CERAMICS INTERNATIONAL Available online at www.sciencedirect.com Ceramics International 41 (2015) 2286–2293 Impacts of Tb substitution at cobalt site on structural, morphological and magnetic properties of cobalt ferrites synthesized via double sintering method Muhammad Azhar Khan a,n , M. Javid ur Rehman a , Khalid Mahmood b , Irshad Ali c , Majid Niaz Akhtar d , Ghulam Murtaza e , Imran Shakir f , Muhammad Farooq Warsi g,n a Department of Physics, The Islamia University of Bahawalpur, Bahawalpur-63100, Pakistan b Department of Physics, GC University Faisalabad, 68000, Pakistan c Department of Physics, Bahauddin Zakaryia University, Multan 60800, Pakistan d Department of Physics, COMSATS Institute of Information Technology, Lahore, 54000, Pakistan. e Department of Physics, Centre for Advanced Studies in Physics, G.C. University, Lahore, Pakistan f Deanship of scientific research, College of Engineering, PO Box 800, King Saud University, Riyadh 11421, Saudi Arabia g Department of Chemistry, The Islamia University of Bahawalpur, Bahawalpur-63100, Pakistan Received 11 September 2014; received in revised form 5 October 2014; accepted 5 October 2014 Available online 12 October 2014 Abstract Cobalt ferrites substituted with terbium (Tb) at cobalt (Co) and iron sites were fabricated by double sintering method and were characterized by the XRD, fourier transform infrared (FTIR) spectroscopy, scanning electron microscope and hysteresis loops measurements. The XRD analyses confirm the formation of single spinel phase for x ¼ 0.0 and thereafter a small peak of secondary phase occurred. The lattice parameter was found to increase by increasing Tb contents and this was attributed to the larger ionic radius of Tb ions as compared to Co ions. FTIR revealed two absorption bands which are characteristic feature of spinel ferrites. The morphology studies exhibit the inhomogeneous grain size distribution. The saturation magnetization was found to exist in the range of 63–67 emu/g and coercivity in the range of 405–435 Oe. The observed variation in saturation magnetization was attributed to the redistribution of cations due to the substitution of terbium at cobalt sites. The incorporation of terbium in cobalt ferrites substantially decreased the coercivity and remanence. The smaller values of coercive field suggest that these materials are potential candidates to be useful in high density data storage devices. & 2014 Elsevier Ltd and Techna Group S.r.l. All rights reserved. Keywords: Co-Tb Ferrites; XRD; FTIR; SEM; VSM 1. Introduction Cobalt ferrite has been in used due to some interesting features like high coercivity, good electrical insulation, high chemical stability and moderate saturation magnetization at room tem- perature. The interest in these ferrites is increasing due to strong magneto elastic effect and their use as energy efficient actuators. Cation substitution as well as heat treatment may affect the physical structure and magnetic properties [1]. Cobalt ferrites become a promising candidate for investigation as an alternative ceramic material for developing novel magnetostrictive smart materials, magneto-optical recording media, magnetic recording and magnetic fluids [2]. These ferrimagnetic spinel ferrites are an important class of magnetic ceramics which have a FCC crystal structure with arrangement of oxygen ions with 64 tetrahedral (A-site) and 32 octahedral interstitial sites (B-site). Out of this, 8 of tetrahedral (A-site) and 16 of octahedral (B-site) sites are occupied by the metal cations. Thus the large fraction of empty interstitial sites makes a considerable open crystal structure which leads to migration of cations among interstitial sites www.elsevier.com/locate/ceramint http://dx.doi.org/10.1016/j.ceramint.2014.10.033 0272-8842/& 2014 Elsevier Ltd and Techna Group S.r.l. All rights reserved. n Corresponding authors. Tel.: þ92 3335121491; fax: þ 92 62 9255474. E-mail addresses: azhar.khan@iub.edu.pk (M.A. Khan), azhar_manais@yahoo.com (M. Farooq Warsi).